Start from Agnew Meadows trailhead. Follow trail past Shadow Lake to Garnett Lake. Stay high above Gannet Lake once in the area and work around left into an obvious meadow drainage system that takes you towards the prominant steep looking left side of Banner. Work up talus until below a thin loose chute. This is where the route begins. About 8-10 miles with 2 - 3000 feet of gain.
We thought this route was really cool. If you want an adventure with alpine conditions but nice rock that isn't well traveled this is it. The setting on the route is phenomenal and it has a Temple Crag feel to it. Calfornia's High Sierra by Moynier and Fiddler provides more info.
Work up the loose chute and over some easy scrambling. Shortly a chimney will be reached and easy face climbing off right will pass it. Now the real climbing starts. Follow the prominent arete (up to 5.6 but easy). Eventually a steep section will be reached and a traverse out right will be necesary (5.7ish). Do this and regain the ridge. From here follow the line of weakness to the summit.
A full rock rack is nice especially if simul-climbing. An ice ax is needed and crampons are recommended.